The present invention relates in general to automatic gear changing systems and in particular to a hydraulic regulating device for load shifted gears, particularly for the automatic transmission in motor vehicles including a plurality of hydraulic coupling elements, a source of pressure fluid, a high pressure conduit connected to the source and a return conduit.
In known hydraulic regulating devices of the above described type each shifting element constituted by a hydraulic coupling of the automatic transmission cooperates with an electromagnetically operated pressure regulating valve having its regulating characteristics proportional to the applied electrical current. In this prior art device, each pressure regulating valve has its pressure port connected to the main high pressure conduit, its return port connected to the reservoir of the pressure fluid, and its working port connected to the assigned shifting element. A suitable electronic control apparatus controls respective pressure regulating valves in such a manner that the desired gear shift condition (forward gear, reverse gear, neutral) of the load shifted gear box be attained. The necessary data for carrying out the proper shift such as the load effect, the vehicle speed or the rotational rate of the engine are detected by corresponding feelers and are fed to the electronic control apparatus which processes the detected data into corresponding control signals for the individual electromagnetically activated pressure regulating valves. As mentioned above, the pressure regulating valves have a current proportional behavior, that means pressure at the output of the pressure regulating valve increases proportionally to the excitation current applied to the actuation solenoid.
This prior art hydraulic control device has the advantage that the individual shifting elements can be individually controlled and regulated by the assigned electromagnetically operated pressure regulating valve without the use of hydraulic controllers and with minimum expenditures in hydraulic circuits. Also the required feelers for sensing rotational speed or the speed of the vehicle and the load effect are simple and can be manufactured at a low cost. The disadvantage of this prior art solution, however, is the fact that the electromagnetically controlled pressure regulating valves having their regulating behavior proportional to the applied electrical current are relatively expensive and consequently the necessity to employ a large number of such pressure regulating valves almost counterbalances the aforementioned advantages.